P027

Code PO27:

PCM Circuit:

DESCRIPTION
This diagnostic test monitors the Idle Speed Control (ISC) Throttle Position (TP) switch during some coast down and idle conditions with the TP switch open and brake applied. Under these conditions, the Powertrain Control Module (PCM) commands the ISC to retract and monitors the TP sensor for a corresponding decrease in throttle position. If the PCM detects a decrease in throttle position two times in succession, then the PCM knows the throttle is resting on the ISC plunger and the (TP) switch should be closed and it sets Code P027.

TEST CONDITIONS
1. Codes P021, PO22 and P024 not set.
2. Vehicle in coast down condition.
3. Throttle position switch open.
4. Brake applied.
5. Throttle angle 16.5 degrees or less.
6. Engine speed at least 64 RPM greater than desired.
7. At least 4 seconds have passed between brake applications or the last ISC motor pulse from the PCM.

FAILURE CONDITIONS
1. The PCM retracts the ISC motor and sees a corresponding decrease in throttle angle twice.

ACTION TAKEN
1. PCM turns "ON" the "Service Engine Soon" Malfunction Indicator Lamp (MIL).
2. PCM disables Exhaust Gas Recirculation (EGR).

NOTES ON FAULT TREE
1. The PCM harness connector of the ISC jumper is located between the generator and cruise control servo.

2. The ISC jumper is a separate harness that connects the ISC to the PCM harness.

NOTES ON INTERMITTENTS
Code PO27 may be set if the Torque Converter Clutch (TCC) Brake Switch is sticking open or the accelerator and brake pedals are depressed simultaneously. Use input switch test PI71 to determine if the brake switch is functioning properly.